Automatic groove tracing method for an arc welding robot

ABSTRACT

A method is disclosed for correcting the travel path of an oscillating robotic welding torch tracing a groove line defined by an upper and lower plate. According to one aspect of the invention, a first integrated value of the welding current at the center of oscillation is compared with second and third integrated values of the welding current at opposite first and second ends of the oscillation, respectively. The travel path of the robotic welding torches adjusted towards the second end of oscillation when the second and third integrated values of the welding current are smaller than the first integrated value of the welding current. According to another aspect of the present invention, a first integrated value of the welding current at the second end of oscillation of a previous oscillation torch is compared with a second integrated value of the welding current at the second end of oscillation of a subsequent oscillation. The travel path of the robotic welding torch is adjusted towards the second end of oscillation when the difference between the first and second integrated value exceeds a predetermined allowable value. According to yet another aspect of the present invention, an integrated value of the welding current at the second end of oscillation is compared with an average integrated value of the second end of oscillation. The average integrated value at the second end of oscillation being a value resulting when the robotic vehicle correctly traverses the groove line. The travel path is adjusted towards the second end of oscillation when the difference between the first and average integrated values exceeds a predetermined allowable deviation value.

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to an automatic tracing method for awelding torch in a lap joint welding operation of a consumable electrodetype arc welding robot.

In the past, as a method for automatically controlling the lap jointwelding of a welding torch 4 of a consumable electrode type arc weldingrobot as shown in FIG. 1, that is, in which an upper plate (web) 2 lapson a lower plate (flange) 3 to define a weld groove line 6, there hasbeen proposed an automatic control method which utilizes the fact that aweld current value varies according to a distance between the weldingtorch 4 and the material to be welded.

The tracing of the weld groove line 6 according to the aforesaid methodis accomplished by oscillating the welding torch widthwise relative thelength of the groove, integrating weld currents at both ends of theoscillation and comparing the thus integrated current values todetermine if they are equal to each other, and moving the oscillationcenter 5 of the welding torch 4 towards the oscillation end having thesmaller of the integrated current values if the values are unequal.

Further, tracing relative the vertical direction of the weld groove line6 is accomplished by comparing an average value of the integratedcurrent values of the weld current with an adequate preset currentvalue, and if the average weld current value is larger than the presetcurrent value, the distance between the welding torch and the materialto be welded is deemed to be too short and therefore an upwardcorrection is made, whereas if the average integrated value of the weldcurrent is smaller than the preset current value, the distance betweenthe welding torch and the material to be welded is deemed to be too longand therefore, a downward correction is made.

However, in the above method of comparing the integrated current valuesat both oscillation ends, then the lap joint welding is as shown in FIG.1, the wall 2 of the upper plate (web) 1 is relatively small, and thewall 2 may become inclined or melted at the lower plate (flange) 3 sideto lose a corner thereof. When the oscillation center 5 of the weldingtorch 4 is deviated from the weld groove line 6 towards the upper plate1, the projected length of a wire 7 on the upper plate 1 side ofoscillation is longer than the projected length of a wire on the lowerplate 3 side of oscillation as indicated by the distance "m". Therefore,the integrated current value on the upper plate 1 side of oscillation issmaller than the integrated current value on the lower plate 3 side ofoscillation, resulting in the issuance of a command for correctiontowards the upper plate 1 side. As a result, an opposite correction ismade in that the oscillation center should be corrected towards thelower plate 3 side to effect the automatic tracing along the weld grooveline 6, resulting in an increase in the deviation from the weld grooveline 6 towards the upper plate 1.

When once departed towards the upper plate 1, the length of the wire 7at the upper plate 1 side of oscillation necessarily becomes long asshown in FIG. 2, and therefore, the weld integrated current value at theoscillation end of the upper plate 1 is small. As a consequence, afurther correction towards the upper plate 1 is effected, and theoscillation center 5 continues to be moved away from the weld grooveline 6.

As a result, an operating state results in which the center ofoscillation departs from the weld line in the automatic tracing method.Due to the occurrence of this phenomenon, the wall 2 of the material tobe welded must be high, as in a T-shape fillet, to accomplish excellentautomatic tracing, but if the material to be welded has a wall 2 whichis liable to be melted, as in a lap fillet, the use thereof isdifficult.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of the above-describedproblem. An object of the present invention is to provide an automatictracing method for a welding torch which can, in a lap fillet welding,prevent a departure towards the upper plate or lower plate without theprovision of a special control device.

For achieving the aforesaid object, the present invention provides anarrangement wherein integrated current values at both ends ofoscillation are compared with an integrated current value of anoscillating center whereby a deviation towards the upper plate isdetected. Alternately, frequency components of a signal having twice theoscillation frequency are extracted and a current phase thereof isdetected to thereby detect a deviation towards the upper plate. Then,correction towards the lower plate is applied irrespective of the resultof comparison between the integrated current values at both ends ofoscillation to prevent a departure toward the upper plate.

According to another embodiment of the invention, a detected weldcurrent is smoothed by a low pass filter having a cutoff frequency equalto a frequency of oscillation, and when the weld current at theoscillation end of the lower plate 1 side significantly increases,correction towards the lower plate is effected irrespective of thecomparison between the integrated current values at both ends ofoscillation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a length of a wire at both ends ofoscillation in the case where a center of oscillation towards an upperplate is deviated in a lap joint welding according to a conventionalmethod.

FIG. 2 is a schematic view showing an oscillating state when a weldingwire runs onto the upper plate.

FIG. 3A is a schematic view where an oscillating center traces a weldgroove line.

FIG. 3B shows a waveform of a weld current relative to FIG. 3A.

FIG. 4A is a schematic view where an oscillating center is considerablydeviated towards the lower plate.

FIG. 4B shows a waveform of a weld current relative to FIG. 4A.

FIG. 5A is a schematic view where an oscillating center is slightlydeviated towards the upper plate.

FIG. 5B shows a waveform of a weld current relative to FIG. 4A.

FIG. 6A is a control flow chart for detecting a deviation towards theupper plate by comparing integrated current values at both ends ofoscillation with an integrated current value at a center of oscillation.

FIG. 6B shows a waveform of a weld current relative to FIG. 6A.

FIG. 7A is a control flow chart for detecting a deviation towards theupper plate by extracting components of a signal having a frequencywhich is twice the oscillation frequency.

FIG. 7B shows a waveform of a weld current relative to FIG. 7A.

FIG. 8 is a schematic view where a clearance is a present in a weldgroove.

FIG. 9 shows a waveform of a weld current relative to FIG. 8.

FIG. 10 is a schematic view showing the state in which an oscillatingcenter is deviated towards the lower plate.

FIG. 11 shows a waveform of a weld current relative to FIG. 10.

FIG. 12 is a sectional view in which a weld bead has formed on the upperplate.

FIG. 13 shows a waveform of a weld current relative to FIG. 12.

FIG. 14 shows a waveform of a weld current from the beginning of arun-on to the upper plate to the completion of a run-on to the upperplate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments for achieving the object of the present invention will nowbe described.

The embodiment described hereinafter is a different control method fromthat using in the conventional device, and for the purpose of betterunderstanding, a principle of the present invention will be firstexplained.

FIG. 3A shows the operating state wherein a torch 4 oscillates along aweld groove line 6, and FIG. 3B schematically shows a waveform of a weldcurrent relative the oscillating torch 4. In this operating state,current values at both ends of oscillation are high, and the currentvalue at the center of oscillation is small in comparison with thecurrent values at both ends of oscillation.

FIG. 4A shows the operating state in which the torch 4 oscillates alonga path that is considerably deviated toward the lower plate 3, and FIG.4B shows a waveform of a weld current in this operating state. As shownin FIG. 4B, the weld current at the oscillation end of the lower plate 3side is largest.

As will be understood from viewing FIG. 3B and FIG. 4B, one of thecurrent values at both ends of oscillation is necessarily larger thanthe current value at the oscillating center.

However, when a deviation towards the upper plate 2 occurs and thecenter position of oscillation is near the edge portion on the upperplate 1 as shown in FIG. 5A, the the current value at the center ofoscillation is larger than the current values at both ends ofoscillation, resulting in the characteristic current waveform shown inFIG. 5B.

Embodiment 1

A first embodiment is based on the knowledge that by detecting aspecific current waveform, a deviation toward the upper plate 1 side canbe recognized, and a correction applied towards the lower plate 3irrespective of a comparison between integrated current values at bothends of oscillation.

In the first embodiment, the welding torch is controlled as shown in theflow chart of FIG. 6A, and the schematic of FIG. 6B, to prevent adeparture towards the upper plate 1.

In the aforesaid first embodiment, in the case where the weld integratedcurrent value in the oscillating center is larger than the weldintegrated current values at both ends of oscillation, the operatingstate in which the welding torch 4 has drifted into upper plate 1 can bedetected.

However, depending on the specific shape of a coupling of a material tobe welded, the quality of material and the welding conditions, even inthe operating state in which the edge of the upper plate 1 has meltedand the welding torch 4 has run onto the upper plate 1, the weldintegrated current value in the oscillating center may sometimes not belarger than the weld integrated current values at both ends ofoscillation.

Therefore, offset values (a and b in the flow chart of FIG. 6A) areapplied to the weld integrated current value of the oscillating center,and then the weld integrated values of oscillation are compared, wherebyeven in the operating state wherein the edge has melted, the running ofthe welding torch 4 onto the upper plate 1 can be detected.

It is also possible to adjust the set amount of the offset to detect theoperating state in which the welding torch 4 has slightly deviatedtoward the upper plate 1.

The offsets a and b have values which vary according to the weldingconditions, and which can be obtained by experiment.

Embodiment 2

A second embodiment is directed to a method for detecting and correctinga deviation towards the upper plate 1 according to a current phaseduring oscillation.

FIG. 7A shows a control flow chart of the second embodiment. FIG. 7Bshows schematic waveforms for a better understanding of the operation ofthe second embodiment.

In the second embodiment, a band pass filter is used for passing asignal having a frequency which is twice the oscillation frequency ofthe welding torch 4, and components of this signal are extracted. Theamplitude of the signal having the frequency which is twice theoscillation frequency is largest when no deviation is present andbecomes smaller as the welding torch 4 is moved from the weld grooveline 6. While the amplitude varies as described above, the phase of thesignal remains constant.

However, as the welding torch 4 deviates towards the upper plate 1, thephase of the current signal having twice the frequency of theoscillation frequency is deviated by a 1/4 wavelength when the center ofthe oscillation is directed on the edge of the upper plate 1 as shown inFIG. 5A.

Therefore, this change in the phase the current signal can be detectedto thereby recognize the state of the welding torch 4 tending to runonto the upper plate 1. In the case where this phase deviation isdetected, and recognition is made of a drifting towards the upper plate1, a correction is applied towards the lower plate 3 regardless of acomparison of the integrated current values at both ends of oscillation,and a departure towards the upper plate 1 can thus be prevented.

Among the two embodiments so far described, in the first embodiment, acomparison is made between the integrated current values at both ends ofoscillation and the integrated current value at the oscillating center,and in the second embodiment the current frequency signal components aredetected to detect the phase thereof, whereby a deviation towards theupper plate 1 can be detected to prevent a departure towards the upperplate 1.

The conventional method for carrying out the oscillated currentdetection is relatively inexpensive and free from interference, and istherefore very effective, but in the case where the conventional methodis applied to the lap joint welding, once a departure towards the upperplate is made, the torch continues to be moved away from a welding line,therefore posing a problem in terms of a reliability.

According to the above-described embodiments of the present invention, adeparture towards the upper plate 1 in a lap joint welding can beprevented by mere software revision, without the use of additionalhardware. Thereby, the reliability of sensing of the lap joint weldingis improved, as well as the sensing of a lap joint welding havingthinner plates.

While two embodiments have been described, modifications and appliedexamples will be described hereinafter.

According to research carried out by the present inventors, after theweld current has been smoothed by a low pass filter for passingfrequencies smaller than the frequency of oscillation, the waveformthereof was verified by experiments, and as a result, it has been foundthat despite the accomplishment of automatic tracing so that the weldintegrated current values at both ends of oscillation are equal to eachother as usual, there occurred a phenomenon wherein a difference betweenthe weld integrated current values at both ends of oscillation isabnormally large. It has been found that the phenomenon could be dividedinto the following three casual types:

(1) where a clearance is present in a groove of a material to be welded;

(2) where a torch tip is greatly deviated from a weld groove line (i.e.,where a position of starting welding is greatly deviated, and where amaterial to be welded is deviated in excess of the ability of automatictracing);

(3) where a weld bead has run on the upper plate.

In the present invention, attention is directed to the state of momentwhere the bead has run-on the upper plate 1, which has been mentionedabove as phenomenon (3), and the current waveform is analyzed to detectthe abnormal phenomenon at a moment when the bead has run on the upperplate 1, thereby preventing the run-on to the upper plate 1.

In order to distinguish the current waveform of phenomenon (3) from theweld current waveforms in the other phenomenons (1) and (2), weldcurrent waveforms for each were analyzed by experimental data.

The results thereof will be described hereinafter.

(i) Weld current waveform at a groove clearance:

The state where a groove clearance is present is schematically shown inFIG. 8, and a corresponding weld current waveform is shown in FIG. 9.

When a clearance "g" is present in a groove between the upper plate 1and the lower plate 3, a weld wire 7 is moved into the clearance "g",and as a result, a short-circuit occurs on the side of the upper plate 1to generate an abnormal current. After the weld, in a portion where amarkedly high weld current in generated on the side of the upper plate1, a large bead 8 is deposited above the clearance. This proves that theshort-circuit occurred to generate an abnormal current.

Therefore, in the weld current waveform A1, as shown in FIG. 9, amarkedly large weld current waveform a₁ appears at a position of signalCw in synchronism with the end of oscillation towards the upper plate 1,and no abnormal phenomenon appears at a position of signal Cf insynchronism with the end of oscillation towards the lower plate 3.

The characteristic of the weld current waveform when a clearance ispresent at a weld groove is thus a markedly large weld current generatedonly when the oscillating end is synchronized with the upper plate 1side.

(ii) Weld current waveform in the case where the oscillating center isdeviated from the weld groove line 6:

In the case wherein the oscillating center 5 is deviated from the startof the welding operation, an abnormal current waveform appears from thebeginning, which can be obviously distinguished.

The oscillating center 5 of the welding torch is greatly deviated fromthe weld groove line 6 more than the ability of tracing in the casewhere it is deviated towards the lower plate 3.

In the case where the oscillating center 5 is deviated towards the upperplate 1, the same condition results as the state wherein the bead runsonto the upper plate, which will be described later in (iii).

In the case where the oscillating center 5 is deviated towards the lowerplate 3, the distance between the welding torch and the material to bewelded becomes longer towards the upper plate 1 side of oscillation, asshown in FIG. 10. Therefore, there appears a waveform as shown in FIG.11 wherein a weld current reduces on the upper plate 1 side ofoscillation. The characteristic of this weld current waveform A2 is thata markedly lower current value a₂ of the weld current waveform occurs ata position of signal Cw in a synchronism with the end of oscillationtowards the upper plate 1.

(iii) Weld current waveform when the oscillating center 5 runs onto theupper plate 1 side:

When the oscillating center 5 of the welding torch is deviated towardsthe upper plate 1, the weld bead runs onto the upper plate 1, as shownin FIG. 12. Also, when the welding torch 4 is oscillated towards thelower plate 3, a large weld current flows.

In this state, when the torch is oscillated towards the lower plate 3,the weld arc does not reach the surface of the lower plate 3, and an arcis generated in a weld pool formed in the edge. That is, the weld pool 9formed in the edge of the upper plate 1 becomes a spherical shape due tosurface tension, and the welding wire 7 assumes a short-circuited stateand a welding current at the end of the lower plate 3 of the oscillationis very large.

FIG. 13 shows a weld current waveform when the center of oscillationruns onto the upper plate 1. The characteristic of the weld currentwaveform A3 is a large weld current waveform a₃ generated at a positionof signal Cf in synchronism with the oscillating end of the lower plate3 side.

The state wherein the edge on the upper plate 1 side is melted into aspherical shape is the characteristic phenomenon generated only when thecenter of the oscillation runs onto the upper plate 1 side during thelap joint welding. Therefore, the characteristic of the large weldcurrent waveform on the lower plate 3 side can be detected to detect thestate of the running-on towards the upper plate 1 side.

When the wire completely runs onto the upper plate 1, the wire becomeslonger towards the upper plate 1 side of oscillation similar to the caseshown in FIG. 2, and therefore, a weld current is smaller at a positionof signal Cw at the oscillation end towards the upper plate 1 sidesimilar to the weld current waveform of FIG. 11. Accordingly, as shownby the weld current waveform A4 of FIG. 14, from the beginning of therunning onto the upper plate 1 side to achievement of completerunning-on, a markedly large weld current waveform a₃ is generated at asignal cf position at the oscillation end towards the lower plate 3 sideas shown in FIG. 4, and thereafter, a small weld current waveform a₂appears at a signal Cw position at the oscillation end towards the upperplate 1 side.

When the phenomenon wherein the weld current waveform becomes large isstudied from the cutoff frequency of a low pass filter, the weld currentwaveform in the state of tracing the groove contains many frequencycomponents twice the frequency of the oscillation frequency, and theweld current waveform in the case where a deviation from a groove ismade is a frequency component of the oscillation frequency, as is wellknown. The the cutoff frequency of the low pass filter is made to bealmost the same as the frequency of the oscillation, the frequencycomponent of twice the oscillation frequency of the weld currentwaveform is cut off by means of a filter in the state of tracing agroove. Therefore, variation in the weld current waveform is small.However, in the state where a deviation from a groove is made, the weldcurrent waveform is a frequency component of the oscillation frequency,and therefore the component is not cut off by the filter and a largeweld current waveform is obtained.

As mentioned above, in the normal automatic tracing operation, theabnormal weld current waveform appears in the case where a clearance ispresent in a weld groove,in the case where a deviation from a grooveline was made, and in the case where running onto the upper plate sidewas made. An abnormally large weld current is generated on the lowerplate side only in the case of the running onto the upper plate side,from which characteristic, the running-on state of the upper plate sidecan be detected.

Accordingly, in the automatic copying accompanied by oscillation, alarge weld current on the oscillating lower plate side generated by therunning-on towards the upper plate is detected an a correction isapplied to the lower plate side irrespective of the comparison betweenthe weld integrated current value of oscillation on the upper plate side1 and the weld integrated value of oscillation on the lower plate 3 sideto thereby prevent a departure towards the upper plate side 1.

An embodiment thereof will be described hereinafter.

The embodiment shown below employs a method for detecting a statewherein a weld current on the lower plate side of oscillation ismarkedly large in order to detect a state of departure towards the upperplate 1 in the automatic copying operation.

Embodiment 3

In the third embodiment according to the present invention, first,automatic copying is effected in a state free from deviation, and anaverage deviation σ of weld integrated current values detected at theoscillation end towards the lower plate side 1. In this case, thedetected weld current is smoothed by a low pass filter for passing afrequency less than that of the oscillation frequency.

In many cases, as will be understood from FIG. 13, a spherical melt pool9 is suddenly formed in an edge of an upper plate 1, indicating state inwhich a large short circuit occurs and a markedly high weld current isgenerated on end of oscillation towards the lower plate 1 side.

Accordingly, a comparison is made between a weld integrated currentvalue Af (N-1) at the oscillation end towards the lower plate side 1 ofa previous oscillation and a weld integrated current value Af (N) of acurrent oscillation, and if a difference {Af (N)-Af (N-1)} therebetweenis larger than an allowable deviation 3σ, a departure state isrecognized.

Embodiment 4

Since the arc welding robot of this type carries out the automatictracing, the weld integrated current value on the upper plate side 1will normally not be very large. Accordingly, in the fourth embodiment,detection is first made of an average value Aw and an average deviationσ of weld integrated current values detected at the end of the upperplate 1 side when automatic copying has been carried out in a state freeof deviations, and a comparison is made between a weld integratedcurrent value Af (N) at the oscillation end towards the lower plate 1side and said average value Aw. If {Af (N)-A2} is larger than anallowable deviation 3σ, a departure state is recognized.

The use of an allowable deviation 3σ in the methods of the third andfourth embodiments is the result of an unevenness of the weld current inthe state free from deviations. This value 3σ is adjusted according tothe welding conditions, such as the welding posture and type ofelectrodes. However, in the normal automatic tracing operation, sincethe weld integrated current value is uneven in a normal distributionmanner, effective detection ban be carried out if an abnormal state isdetected with 3σ as a reference allowable deviation.

When a departure state is recognized by either method as describedabove, the device is pulled back towards the lower plate 3 by a largecorrection amount corresponding to two to five times the correctionamount of the normal automatic tracing operation, irrespective of thecompared value of the integrated current values at both ends ofoscillation, to prevent a departure towards the upper plate 1 side.

As described above, in the present invention, the state wherein a weldcurrent at the lower plate 3 side during oscillation is markedly largeis detected to effect a correction toward the lower plate 3, whereby adeparture toward the upper plate 1 in the lap joint welding can beprevented.

Further, the method for detecting a weld current at the oscillating endto effect tracing is relatively inexpensive and free from interferencenear a welding torch and is very effective. However, in the case wherethe aforesaid is applied to a lap joint welding, if a departure towardsthe upper plate 1 occurrence once, the torch continues to move away froma weld groove line, thus giving rise to a problem of reliability.However, according to the present invention, there are effects in that adeparture towards the upper plate can be prevented without us ofadditional hardware, reliability in sensing of a lap joint welding isimproved, and sensing of a lap joint welding for sheets is alsopossible.

We claim:
 1. A method of correcting the travel path of an oscillatingrobotic welding torch, said robotic welding torch tracing a groove linedefined by an upper and lower plate and oscillating laterally relativesaid groove line to define a center of oscillation and opposite firstand second ends of oscillation, said first end of oscillation extendingtowards the upper plate and said second end of oscillation extendingtowards the lower plate, said robotic welding torch further having awelding current which has a value related to a distance between therobotic welding torch and the upper and lower plate, said methodcomprising the steps of:measuring a first integrated value of thewelding current at the center of oscillation of the robotic weldingtorch; measuring a second integrated value of the welding current at thefirst end of oscillation of the robotic welding torch; measuring a thirdintegrated value of the welding current at the second end of oscillationof the robotic welding torch; comparing the first integrated value ofthe welding current with the second and third integrated values of thewelding current; adjusting the travel path of the robotic welding torchin a direction towards the second end of oscillation when the second andthird integrated values of the welding current are smaller than thefirst integrated value of the welding current.
 2. A method of correctingthe travel path of an oscillating robotic welding torch, said roboticwelding torch tracing a groove line defined by an upper and lower plateand oscillating laterally relative said groove line to define a centerof oscillation and opposite first and second ends of oscillation, saidfirst end of oscillation extending towards the upper plate and saidsecond end of oscillation extending towards the lower plate, saidrobotic welding torch further having a welding current which has a valuerelated to a distance between the robotic welding torch and the upperand lower plate, said method comprising the steps of:passing a signalindicative of the value of the welding current through a low pass filterhaving a cut-off frequency which is nearly the same as an oscillationfrequency of the robotic welding torch; comparing a first integratedvalue of the welding current at the second end of oscillation of aprevious oscillation of the robotic welding torch with a secondintegrated value of the welding current at the second end of oscillationof a subsequent oscillation of the robotic welding torch; adjusting thetravel path of the robotic welding torch in a direction towards thesecond end of oscillation when a difference between the first and secondintegrated values exceeds a predetermined allowable deviation value. 3.A method as recited in claim 2, wherein the predetermined allowabledeviation value substantially equals three times an average deviationvalue, the average deviation value equalling an average deviation of thewelding current at the second end of oscillation when the roboticwelding torch correctly traces along the groove line.
 4. A method ofcorrecting the travel path of an oscillating robotic welding torch, saidrobotic welding torch tracing a groove line defined by an upper andlower plate and oscillating laterally relative said groove line todefine a center of oscillation and opposite first and second ends ofoscillation, said first end of oscillation extending towards the upperplate and said second end of oscillation extending towards the lowerplate, said robotic welding torch further having a welding current whichhas a value related to a distance between the robotic welding torch andthe upper and lower plate, said method comprising the steps of:passing asignal indicative of the value of the welding current through a low passfilter having a cut-off frequency which is nearly the same as anoscillation frequency of the robotic welding torch; comparing a firstintegrated value of the welding current at the second end of oscillationof the robotic welding torch with a second integrated value, said secondintegrated value being an average integrated value of the weldingcurrent at the second end of oscillation when the robotic welding torchcorrectly traces along the groove line; adjusting the travel path of therobotic welding torch in a direction towards the second end ofoscillation when a difference between the first and second integratedvalues exceeds a predetermined allowable deviation value.
 5. A method asrecited in claim 4, wherein the predetermined allowable deviation valuesubstantially equals three times an average deviation value, the averagedeviation value equalling an average deviation of the welding current atthe second end of oscillation when the robotic welding torch correctlytraces along the groove line.